A background art will be described with reference to FIGS. 5, 6A, and 6B. As shown in FIG. 5, a thermal acoustic effect is caused by a sound wave. Specifically, a sound wave causes adiabatic compression of air and adiabatic expansion of air to generate acoustic energy, thereby to radiate heat on a compression side and to absorb heat on an expansion side. More specifically, an acoustic stack is employed to utilize a sound wave to cause adiabatic compression of air and adiabatic expansion of air thereby to cause a temperature gradient by utilizing the thermal acoustic effect. The acoustic stack causes difference in temperature at both ends due to heat absorption and heat radiation.
For example, Patent Document 1 discloses a configuration to cool intake air, which flows through the intake passage 101, by utilizing acoustic energy in an intake passage 101. More specifically, the configuration of Patent Document 1 cools intake air by utilizing sound wave energy caused by pulsation in intake air.
It is noted that, the configuration of Patent Document 1 may cause pressure loss in intake air and/or noise.
(Patent Document 1)
Publication of unexamined Japanese patent application No. 2007-270619